1. Field of the Invention
The present invention relates to ingredients for use in propellant and gas generant compositions, and more specifically to fuels containing a high oxygen balance. The fuels are useful in smokeless, reduced smoke and metallized rocket propellants, gun propellants, and gas generants for engine starter cartridges, cartridge actuated devices, pressurization of liquid rocket propellant tanks, aircraft ejection seats, piston operated mechanical devices, air bag occupant restraint systems for automobiles, inflation and expulsion devices, flotation devices, and fire suppression devices.
2. Background Art
There is high demand for propellant and gas generant compositions that on combustion yield acceptable burning rates and provide, at relatively low flame temperatures, a high volume of substantially non-toxic gas and a low volume of solid particulate matter that can produce smoke. It is important that resulting solid by-products from the combustion of solid propellant compositions be minimal, and the gaseous combustion products be substantially non-toxic, and non-corrosive. Various compositions of propellants and gas generants have been utilized in the past in an attempt to reach the above desirable characteristics.
Prior art low vulnerability Class 1.3, minimum smoke and reduced smoke propellant compositions have been based on ammonium nitrate, but these compositions exhibit low burning rates and require the use of phase stabilizers in the oxidizer which results in formation of solid particulates in the exhaust.
Propellant compositions have also been developed to include the addition of modifiers to lower flame temperatures and increase gas production. Further ingredients may be added such as binders, ignition aids, slag formers, scavengers, and catalysts to improve various features of the underlying propellant. The modifiers and additional ingredients often times, however, improve one aspect of the propellant composition while also contributing to the production of undesirable by-products, and may increase the corrosiveness thereof. This is particularly disadvantageous for propulsion or mechanical device which require a high pressure gas in order to function properly, examples of which include guns, rocket motors, liquid propellant fuel tanks, jet engines, inflation devices, etc.
U.S. Pat. No. 5,386,775 discloses an azide-free gas generant composition for inflating an automobile or aircraft occupant safety restraint bag that allegedly reduces the toxicity of the gases produced by the gas generants. Specifically, a relatively low energy nitrogen containing fuel is combined with a burn rate accelator, such as an alkali metal salt. The fuel may be guanidine mononitrate, oxamide, ammonium oxalate, aminoguanidine bicarbonate, glycine nitrate, hydrazodicarbonamide or azodicarbonamide.
U.S. Pat. No. 5,608,183 discloses a gas generant composition containing amine nitrates and basic copper nitrate and/or cobalt triamine trinitrate. This gas generant composition was produced as an alternative to non-azide gas generant formulations.
U.S. Pat. No. 2,929,698 discloses an explosive composition produced from a diaminoguanidine mononitrate, monoperchlorate, or monopicrate salt of an acidic agent such as nitric acid, perchloric acid, or picric acid. The present invention pertains to propellant or gas generant compositions (not explosives) containing high oxygen balance fuels based on monoaminoguanidine, diaminoguanidine, and triaminoguanidine dinitrate salts of nitric acid. The mononitrate salts disclosed in the '698 patent do not exhibit a high oxygen balance exhibited by the present invention. Without the high oxygen balance achieved with the fuels of the present invention, a greater concentration of an oxidizer, such as phase-stabilized ammonium nitrate (PSAN), ammonium perchlorate (AP), or potassium perchlorate (KP) would be necessary to maintain an acceptable oxygen to fuel ratio. This would result in lower performance and a significantly greater concentration of corrosive gas or smoke particulates in the exhaust.
One major gas generating composition having desirable characteristics for use in inflation systems contains strontium nitrate and 5-aminotetrazole (SrN/5ATZ) as major constituents. This formulation is relatively non-toxic when compared with sodium azide systems, has good ballistic properties, and retains the majority of solid combustion products as a slag or clinker in the combustion or filtration areas of the inflator unit. These formulations also exhibit acceptable flame temperatures of 2250.degree. K. to 2750.degree. K., depending upon the stoichiometry of the formulation and the oxygen-to-fuel (O/F) ratio. Moreover, the strontium nitrate and 5-aminotetrazole formulations are relatively non-hygroscopic and the ingredients do not exhibit crystalline phase changes over the required operating temperature range.
Such a formulation, however, suffers with regard to gas output, especially, in the volume-limited systems of a driver's side air bag. This is because a high concentration of strontium nitrate is required to maintain a neutral O/F balance. Because inflator designs for use with automotive safety restraint systems are becoming smaller and thus, more volume-limited, propellants are required to provide greater gas output and still retain the desirable attributes of the strontium nitrate/5-aminotetrazole systems. In addition, the SrN/5ATZ compositions are not practical for use in gun systems, rocket systems, jet engine starter cartridges because of the low performance and high concentration of solid decomposition products formed during combustion.
Approaches have been taken to obtain the attractive features of the above-noted propellants, while overcoming the low gas and high solids output thereof. This has resulted in the development of propellants based on mixtures of potassium perchlorate and oxygenated fuels such as guanidine mononitrate and aminoguanidine mononitrate. These propellants are also relatively non-hygroscopic, provide excellent gas output, high burning rates, and only about two thirds of the solid combustion products of the above-noted strontium nitrate and 5-aminotetrazole based propellants. Unfortunately, for use in rocket and gun systems, these formulations still suffer from excessive solid combustion products. In air bag systems, the solid combustion products do not form clinkers or slags that deposit in the combustion or filtration area, but instead form very fine particulates in the gas stream that result in a smokey and dirty exhaust.
Smokey or dirty exhaust combustion products are not militarily or commercially desirable. This is particularly true for military weapons systems where detection by an adversary of the launch position of a missile is unacceptable. It is also true for automobile air bag systems because the production of such product may cause undue anxiety for drivers and passengers involved in an automobile accident in which air bags are deployed. As a result, there is a need for a propellant material or gas generant for use in a variety of applications that exhibits high gas output and performance upon combustion, but does not produce unwanted by-products upon combustion.